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791b350dc7
If the compiler reduces the stack usage in function f1 before calling into function f2, then when we swapcontext back to f1 and continue execution we may overwrite registers that were spilled to the stack while f2 was executing. Later when we return to f2 the corrupt registers will be reloaded from the stack and the test will crash. This was most commonly observed on i686 with __x86.get_pc_thunk.dx and needing to save and restore $edx. Overall i686 has few registers and the spilling to the stack is bound to happen, therefore the solution to making this test robust is to split function f1 into two parts f1a and f1b, and allocate f1b it's own stack such that subsequent execution does not overwrite the stack in use by function f2. Tested on i686 and x86_64. Signed-off-by: Carlos O'Donell <carlos@redhat.com>
131 lines
3.3 KiB
C
131 lines
3.3 KiB
C
/* Check setcontext on the context from makecontext.
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Copyright (C) 2018 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<http://www.gnu.org/licenses/>. */
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#include <stdio.h>
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#include <stdlib.h>
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#include <ucontext.h>
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#include <unistd.h>
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#include <stdatomic.h>
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static ucontext_t ctx[5];
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static atomic_int done;
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static void
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__attribute__((noinline, noclone))
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f2 (void)
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{
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done++;
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puts ("swap contexts in f2");
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if (swapcontext (&ctx[4], &ctx[2]) != 0)
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{
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printf ("%s: setcontext: %m\n", __FUNCTION__);
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exit (EXIT_FAILURE);
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}
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puts ("end f2");
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exit (done == 2 ? EXIT_SUCCESS : EXIT_FAILURE);
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}
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static void
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f1b (void)
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{
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if (done)
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{
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puts ("set context in f1b");
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if (setcontext (&ctx[3]) != 0)
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{
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printf ("%s: setcontext: %m\n", __FUNCTION__);
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exit (EXIT_FAILURE);
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}
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}
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exit (EXIT_FAILURE);
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}
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static void
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f1a (void)
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{
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char st2[32768];
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puts ("start f1a");
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if (getcontext (&ctx[2]) != 0)
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{
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printf ("%s: getcontext: %m\n", __FUNCTION__);
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exit (EXIT_FAILURE);
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}
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ctx[2].uc_stack.ss_sp = st2;
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ctx[2].uc_stack.ss_size = sizeof st2;
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ctx[2].uc_link = &ctx[0];
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makecontext (&ctx[2], (void (*) (void)) f1b, 0);
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f2 ();
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}
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/* The execution path through the test looks like this:
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do_test (call)
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-> "making contexts"
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-> "swap contexts"
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f1a (via swapcontext to ctx[1], with alternate stack)
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-> "start f1a"
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f2 (call)
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-> "swap contexts in f2"
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f1b (via swapcontext to ctx[2], with alternate stack)
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-> "set context in f1b"
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do_test (via setcontext to ctx[3], main stack)
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-> "setcontext"
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f2 (via setcontext to ctx[4], with alternate stack)
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-> "end f2"
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We must use an alternate stack for f1b, because if we don't then the
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result of executing an earlier caller may overwrite registers
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spilled to the stack in f2. */
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static int
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do_test (void)
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{
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char st1[32768];
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puts ("making contexts");
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if (getcontext (&ctx[0]) != 0)
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{
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printf ("%s: getcontext: %m\n", __FUNCTION__);
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exit (EXIT_FAILURE);
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}
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if (getcontext (&ctx[1]) != 0)
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{
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printf ("%s: getcontext: %m\n", __FUNCTION__);
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exit (EXIT_FAILURE);
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}
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ctx[1].uc_stack.ss_sp = st1;
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ctx[1].uc_stack.ss_size = sizeof st1;
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ctx[1].uc_link = &ctx[0];
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makecontext (&ctx[1], (void (*) (void)) f1a, 0);
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puts ("swap contexts");
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if (swapcontext (&ctx[3], &ctx[1]) != 0)
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{
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printf ("%s: setcontext: %m\n", __FUNCTION__);
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exit (EXIT_FAILURE);
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}
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if (done != 1)
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exit (EXIT_FAILURE);
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done++;
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puts ("set context");
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if (setcontext (&ctx[4]) != 0)
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{
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printf ("%s: setcontext: %m\n", __FUNCTION__);
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exit (EXIT_FAILURE);
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}
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exit (EXIT_FAILURE);
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}
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#include <support/test-driver.c>
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